Study of rodlike homopolypeptides by gel permeation chromatography with light scattering detection: Validity of universal calibration and stiffness assessment

Gel permeation chromatography with simultaneous light scattering measurements has been performed on poly(gamma -benzyl-alpha -L-glutamate) and poly(gamma -stearyl-alpha -L-glutamate) in N,N'-dimethylformamide and tetrahydrofuran, respectively. Intrinsic viscosities were computed by combining the measured molecular weights with literature values for the Mark-Houwink parameters. The product of intrinsic viscosity and molecular weight for the rodlike polymers, when plotted against elution volume, overlaid the results for polystyrene, a random coil. In the excluded-volume limit, similar convergence was observed for the second virial coefficient of osmotic pressure as a function of polymer number density. In the case of poly(gamma -benzyl-alpha -L-glutamate) the radius of gyration increased linearly with mass up to at least M = 100 000, corresponding to a contour length of 70 nm. Slight deviations from linear behavior at higher mass suggest a persistence length in the upper range of literature values based on measurements that did not have the advantage of chromatographic separation.